The invention relates to a fluid friction clutch of the type having a cup disk, a housing surrounding the cup disk forming a working chamber formed as a cylindrical ring gap with a circumferential surface of the cup disk. A surrounding clutch fluid collecting groove with a back pressure body and a return flow duct are provided for accommodating pumping of clutch fluid between the working chamber and a storage chamber.
A fluid friction clutch of this type is known (DE 30 41 829 C2). In this known clutch construction, thread-type grooves are provided in the cylindrical circumferential surface of the cup disk which have the purpose of conveying the clutch fluid located in the working chamber through the ring-shaped shearing gap between the cup disk and the housing to a collecting groove and from there, by way of a back-pressure body, back into the storage chamber. This measure is required particularly in the case of high performances because the circulation of the clutch fluid is very important with respect to the necessary cooling. In order to compensate the disadvantage of the low height of the ring-shaped shearing gap at the cylindrical transmission surface, the thread-type grooves are provided. However, the manufacturing of the cup disks for such a fluid friction clutch is relatively expensive. As a result of the arrangement of the collecting groove which still projects into the cylindrical area of the circumferential surface of the cup disk, the effective transmission surface is also reduced by the amount of the groove width.
An object of the invention is to develop a fluid friction clutch of the initially mentioned type in such a manner that the quantity of the circulating clutch fluid becomes as large as possible but without the requirement of thread-type grooves in the circumferential surface of the cup disk or of other expensive measures.
In order to achieve this object, an arrangement is provided wherein the cup disk is provided with an edge portion extending radially outwardly of the circumferential surface and projecting into the surrounding collecting groove. By means of this development, the shearing gap with respect to the cylindrical circumferential surface of the cup disk, in its front area, is shifted slightly radially toward the outside. Because of the fact that the space of the collecting groove is therefore set off from the actual working space to a larger diameter toward the outside, it is ensured that the clutch fluid, which affects the torque transmission, is completely withdrawn from the working gap. This measure therefore permits the circulating of a large quantity of clutch fluid without requiring costly measures for this purpose.
The conveying of the clutch fluid back into the storage space is also promoted in especially preferred embodiments wherein the front face of the cup disk is provided with radially extending grooves which lead into a circumferential surface of the edge. In certain preferred embodiments at least three grooves are provided uniformly around the circumference of the cup disk. The radial grooves, which lead radially into the area of the edge and its circumferential surface, exercise an additional pumping effect and provide mainly that, even in the case of small rotational speed differences, the clutch fluid located in the gap between the front face of the cup disk and the partition moves radially toward the outside, while always wetting the working gap in a uniform manner and thus providing that rotational speed fluctuations, particularly in the case of a small amount of fluid, are excluded as much as possible.
In certain preferred embodiments of the new fluid friction clutch, arrangements are provided wherein conical openings are provided in a radially exterior area of the cup disk, in which the grooves are also arranged and located on a diameter which is larger than the diameter on which the inlet opening means is located and wherein the center points of the conical openings are located on a circle on which the center points of the radii (r) which close off the grooves radially toward the inside are also located. These features result in the advantage that the clutch fluid, which flows in from the inlet bore in a temperature-controlled manner, can also reach the rear area of the cup disk and the rear area of the working chamber as fast as possible. For this purpose, the conical bores are arranged on a radius which is identical to or larger than that on which the inlet opening is located.
Certain preferred embodiments include arrangements wherein axially or approximately axially extending notches are provided which lead into the collecting groove in the ring surface of the housing which extends in parallel to the circumferential surface of the cup disk. Also arrangements are provided wherein the notches are provided with a profile of varying depth (t.sub.1, t.sub.2), the largest depth (t.sub.1) of the notches being located in the area of the collecting groove. These features result in the advantage that the wetting of the transmission surfaces with the clutch fluid is promoted, as mentioned above, in the case of a working gap, which as a rule is very narrow, for example, 0.2 mm. The axially extending notches can easily fill with the clutch fluid and therefore provide a uniformly increasing wetting. The conical shape of these notches results in an advantageous conveying effect in the direction of the collecting groove.
Especially preferred embodiments are also provided wherein the diameter (D) of the edge of the cup disk corresponds to approximately the diameter on which the tread of the axially extending notches is located at the point of their greatest depth (t.sub.1), and wherein the edge of the cup disk has an axial width (b) which corresponds to approximately the width (a) of the back-pressure body means such embodiments have proven to be particularly effective for the method of operation of the new clutch.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.